That depends on his "top gear" equipment, a GTX 670 isn't optimal for Skyrim mods.
Skyrim mods eat your videocards VRAM like it's candy, for heavy Skyrim modding a single AMD 7950/7970 would do a lot better than a GTX 670.
7970: 3GB VRAM.
670: 2GB VRAM
Another option here could be the Powercolor HD 7970 Devil 13 card www.techpowerup.com/reviews/Powercolor/HD_7990_Devil_13/

It should be able to make these mods playable with it's double 7970 cores and 6GB of VRAM.

That or you could just get one of the 6GB 7970 versions out there on sale.
Pro tip: a GTX 670/680 with 4GB of VRAM would still be kicked by a 7970. The 670/680 cards memory bandwith is too low to handle the RAM usage properly.

That and a i5 2500K at 4GH isn't top of ht eline anymore, got a i5 3570k/i7 3770k if you plan on playing Skyrim with heavy modding.